With absorbent products being made super thin, such technologies as making SAP into a sheet form have become very important. Among such technologies, as a promising process, an attempt has been made to prepare a slurry by dispersing SAP in water, an organic solvent or an organic solvent/water mixed solvent using a viscosity adjusting agent such as CMC, MFC and PEO for coating a support. For example, in Patent Application Laid-open Hei 10-168230, an example where a coater and a kiss coater of a grid form, in Patent Application Laid-open Hei 11-34200, an example where coating is conducted from a nozzle of a tube type, in Patent Application Laid-open Hei 11-128825, an example where a die coater, a curtain coater, a knife coater or a spray coater is used, in Patent Application Laid open Hei 11-226467, an example where a slurry is guided from a buffer tank through to an overflow nozzle and in Japanese Patent Application Laid-open 2000-5674, an example where a pattern coating is conducted using a contact head are disclosed respectively.
In coating various types of substrate surfaces, the dispersion slurry in which solid particles are dispersed in a dispersion medium, unlike the case where a liquid to be applied for coating is a uniform solvent, is apt to have some partial variation in concentration due to phase separation, settling down, agglomeration and the like. In case the dispersion slurry is applied for coating, it is preferable to utilize a low cost roll coater of a relatively simple structure among various coaters available, but with such roll coater dispersed solid particles are apt to settle down in the dispersion slurry or to adhere to the surface of a coating roll. If such settling down or adhesion takes place, the coated surface may be uneven or clogging may take place during operation so that it becomes difficult to run a uniform and stable coating operation.
In order to diminish the settling down and adhesion of the dispersed solid particles, such actions for establishing making a condition where slurry may be made easier to be detached have been taken like treating of the surface of a coating roll with a material such as silicone and Teflon (registered trademark), scraping by means of a scraper, and rotating of a roll in a positive direction or a reverse direction.
Compared with such solid containing dispersion slurry, since the slurry in which SAP is dispersed is less fluid and thus apt to get of sludge like, it becomes more difficult to obtain stable and uniform coating with such SAP dispersion slurry and so far no commercial process therefor has been developed yet.